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SubjectRe: [PATCH] KVM: X86: Fix dereference null cpufreq policy
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On 02/03/20 09:12, Viresh Kumar wrote:
> On 02-03-20, 08:55, Paolo Bonzini wrote:
>> On 02/03/20 08:15, Wanpeng Li wrote:
>>> From: Wanpeng Li <wanpengli@tencent.com>
>>>
>>> cpufreq policy which is get by cpufreq_cpu_get() can be NULL if it is failure,
>>> this patch takes care of it.
>>>
>>> Fixes: aaec7c03de (KVM: x86: avoid useless copy of cpufreq policy)
>>> Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
>>> Cc: Naresh Kamboju <naresh.kamboju@linaro.org>
>>> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
>>
>> My bad, I checked kobject_put but didn't check that kobj is first in
>> struct cpufreq_policy.
>>
>> I think we should do this in cpufreq_cpu_put or, even better, move the
>> kobject struct first in struct cpufreq_policy. Rafael, Viresh, any
>> objection?
>>
>> Paolo
>>
>>> policy = cpufreq_cpu_get(cpu);
>>> - if (policy && policy->cpuinfo.max_freq)
>>> - max_tsc_khz = policy->cpuinfo.max_freq;
>>> + if (policy) {
>>> + if (policy->cpuinfo.max_freq)
>>> + max_tsc_khz = policy->cpuinfo.max_freq;
>>> + cpufreq_cpu_put(policy);
>>> + }
>
> I think this change makes sense and I am not sure why should we even
> try to support cpufreq_cpu_put(NULL).

For the same reason why we support kfree(NULL) and kobject_put(NULL)?

Paolo

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